The present invention relates to an upwelling-generating structure, and more particularly to a mound-shaped upwelling-generating structure set on the seabed. The commonly called upwelling that flows from a deep sea zone to a surface sea zone and that is low in temperature and high in specific gravity thrusts upward deep sea water liable to stagnate, thus developing the exchange of the sea water between the deep zone and the surface zone.
The upwelling also thrusts upward abundant resources of nutrient salts such as phosphates and nitrates in the deep zone of the sea water to the upper zone where the sunlight can be reached, thus developing the assimilation of solar photosynthesis and breeding of plankton in the sea water, while at the same time the difference in water pressure and temperature between the deep zone and the surface zone that thrusts upward the cold water in the deep zone to the surface zone enriches the amount of dissolved oxygen, thereby generating an inhabitable environment for fish.
Accordingly, if it is possible to make use of a horizontal flow of water such as ocean current or tidal current in order to generate vertical upwelling, it is very worth of trying to realize, and in fact many different types of structures have been developed for generating an upwelling flow from a horizontal flow.
As an example of prior art structures, Japanese Laid-open Utility Model Application No. 27482/1987 discloses a block structure 150 for artificial reef FIG. 18). As shown in FIGS. 18 and 19, a shielding plate 151 is installed perpendicularly to a tidal current A. According to this invention, the tidal current that collides with the shielding plate 151 rides across the shielding plate 151, while at the same time the tidal current generates a negative pressure area behind the shielding plate 151 where tidal currents A" that flows down along side plates 152 are drawn in. The tidal currents A" thus drawn in from both sides collide with each other to generate whirlpools, thereby causing the tidal current A' that rides across the shielding plate 151 to be oriented upward so that as a whole a large upwelling current is generated.
Another example of prior art structures, as is shown in FIG. 21, is a vertical V-shape structure 160 to form spiral streams 162 at both edges 161 thereof and the spiral streams 162 thus formed join together to generate horseshoe whirlpools 163 downstream. These horseshoe whirlpools 163 are more intensified by a tidal current B' that rides across plates 164, and after some of them join together in a peeling zone behind the plates 164, they flow downstream. In such downflow process, since these horseshoe whirlpools 163 have an upward self-induced velocity, heads of these horseshoe whirlpools ascend and finally all of these whirlpools as a whole ascend nearly vertically. Further, when such state of these horseshoe whirlpools is reached, the direction of the self-induced velocity is reversed backward so that a difference is velocity is caused between these horseshoe whirlpools and their surrounding flows, and this velocity difference causes heads of the horseshoe whirlpools to give upward lift, thus ascending more and more.
However, there is a problem that according to such prior art structures, since the tidal current A, as shown in FIG. 18, collides nearly perpendicularly with the shielding plate 151 at the artificial reef block 150, as shown in FIG. 20, a reverse current zone 154 grows which occurs in the upstream side of the shielding plate 151, thus making it impossible to change a horizontal flow efficiently to a vertical flow.
There is another problem that the V-shape structure 160 shown in FIG. 21 can create high upwelling only for one-directional flow moving toward a V-shape concave opening 165. To cope with a reciprocating stream that is caused by tidal ebb and flow, as an example, even the use of a W-shape or corrugated structure, as is shown in FIG. 22, does not create the spiral stream that causes the upwelling at both edges 168 of opening 167, thus being unable to expect considerable upwelling.
There is a further problem that since a vertical structure such as artificial reef block 150 or V-shape structure 160 has a large single body of structure, it is difficult to draw the structure into a deep seabed to install and further to recover the structure that turns down after installed.